Usually pronounced "stef" when said aloud, which it hardly ever is, stf is a now rarely used abbreviation for scientifiction, chiefly employed today in its adjectival form, stfnal (pronounced "STEF-nel" or "STIF-nel"), which applies to anything science-fictional or part of the microcosm.

In fandom, stfnal has positive (though deliberately slightly archaic) connotations, while skiffy is mildly negative (it's usually used humorously) and sci-fi denotes disapproval or shows ignorance.

(Hogenmiller:Ackerman) Formerly the abbreviation for Scientifiction, now pronounced "stef" or in a number of ways which George Charters reviews below. (It is NOT pronounced "ess tee eff"!!!) It is now a short form for science-fiction, and in the form stfsy for science-fiction AND fantasy — i e the whole field of fantasy writing. Adjectival form stfnal means pertaining to science-fiction, or sometimes to fandom. "St(e)fnist" was (1) proposed by Speer as a substitute for "fan" on account of the undesirable connotations of the latter word, but has come to mean (2) any person interested in fantasy — fans, pros, and mere occasional readers. Such folk have also been described as the stfnate, and rarely stfim.

Some fans wonder, "What's the diff?"
They don't care if you call it stf.
But some, whose noise would make you deaf
Vociferously yell for stf.
The non-fan says, "A lotta guff —
It's obviously only stf."
Myself, I laugh a scornful laugh;
I think the damn thing might be stf.James White prefers to stand aloof,
But, pressed, he coyly murmurs "stf".Bob Shaw just shrugs the matter off.
For all he cares, it could be stf.
And Walter Willis and his wife
Say "Erudition calls for stf."